Global resistive MHD calculations for high-beta DIII-D divertor tokamak

Abstract

Summary form only. The linear and nonlinear resistive MHD phenomena for finite- beta ( beta is the ratio of plasma pressure to toroidal magnetic field energy) noncircular tokamak equilibria have been studied using a 3-D initial-value code, CART. The code, which uses Cartesian coordinate mesh, is particularly suited for treating noncircular shapes, up-down asymmetry, open field lines, and a magnetic separatrix, all of which characterize realistic DIII-D single-null divertor discharges with high pressure or high current. More than two dozen magnetic signals calculated from inferred profiles have shown good agreement with measurements in both relative amplitudes and phases when the vacuum vessel is treated as conducting and its exact noncircular shape is taken into account. The calculations suggest that the prevailing mode structure of the pressure-driven resistive mode could change from short to long wavelength as the plasma pressure is increased, in accordance with experimental observation. The line-tying effect in terms of reduced resistivity in open field lines and the localized change in the interior resistivity due to local heating have been found to have some weak effect on these global resistive MHD modes for the DIII-D plasmas. >